Thermionic cathode construction



july 22,1947- v w.w.wATRoUs,JR 2,424,293

THERMIONIG CATHODE CONSTRUCTION,

Filed Marh 9, 1944 2 Sheets-5h96?. 1

INVENTOR IKW. Wma, we.

BY mmm ArroRNEY W. W. WATROUS, JR

THERMIONIG CATHODE CONSTRUCTION I Filed March 9, 1944 July 22, 1947.

2 Sheets-Sheet 2 fop 1 I.

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' I BY www ATTORNEY Patented July 22, 1947 2,424,293 THERMONIC CATHODE CONSTRUCTION Ward W.'Watrous, Jr., Chatham,

N. .J assignor to Westinghouse Electric Corporation, .East Pittsburgh, Pa., a corporation oLPennsylvania Application March 9, 1944,:

16 Claims.

This invention relates to electrical discharge devices, and more particularly to a novel form of cathode heater and heater-containing cathode.

The primary object of my invention, generally considered, is to provide an improved cathode heater and the cathode using the same, avoiding some of the objections of former types of indirectly-heated cathodes.

Another object of my invention is th'e provision of va cathode heater comprising a, refractory insulated core, a helical heater wire portion on the outside and a straight heater wire portion on the inside of said core.

A further object vof my invention is the pro- 'vision of an indirectly-heated cathode with a `heater as above described and contained in a hol- -low cylindrical element thereof defining a heaterreceiving space, saidheater being held in place with respect to said element by top and bottom cap portions, the former portion with an embossment receiving thetop of the core and a depending peripheral flange secured to said cylindrical element, and the latter portion gripping the core in a groove therein and with a dependent peripheral flange also secured to said cylindrical element.

A still further object of my invention is the provision of an extremely simple cathode heater assembly requiring no insulating coating, giving uniform cathode heating, that is, with a minimum temperature gradient from the top to the bottom of the cathode, and because of low mass, heating said cathode faster than previously.

Other objects and advantages of the invention, relating to the particular arrangement and construction oi the various parts, will become apparent as the rdescription proceeds.

lReferring tothe scale drawing:

Fig. 1 is an elevational view, with parts broken away, of, a thyratron embodying my invention.

'Fig 2 is an axial sectional scale of the cathode of. said thyratron, with heater coil and` core shown inelevation.

Fig. 3 is a transverse sectional viewon the line III- III of'Fig. 2, in the direction of the arrows.

Fig. 4 is an view on a larger the enlarged elevational view of the cathode heating element.

Fig. 5 is a plan of heating element sh'own in Fig. 4.

Fig; 6 is a diagram illustrating-why thecathode SeriallNo. 525,659

(Cl. Z50-27.5)

operates at substantially uniform temperature along its axis.

along the axis of thel cathode.

' opposite- In accordancewvith my invention Iprovide la cathode heater which:

(I) Has no insulatingcoating.

(II) Gives uniform cathode heating, vthat is, a minimum temperaturegradient from the topto the bottom of the cathode.

(III) vProvides fasterheating due to low thermal mass.

(IV) Is extremely simple in construction.

I will nowV describe a thyratron in which` one embodiment of my cathode heater isv employed, it being understood, however, that such a heater is ,adapted lfor many devices having indirectlyheated cathodes.

`Referring to the drawing in detail, there .is shown a thyratron II comprising a glass or vitreous envelopeV I2' which -is evacuated and provided witn' a small quantity ofrilling material, such as mercury Vapor or inert gas. Theenvelope is provided with a re-entrant stem I3 through the press. I4 of which extend lead wires makingv connection I5 on the bottom of .an attached .base IB.A '.The end of vthe envelope is constricted and capped with a terminal member I'I, which ,makes connection with a depending rod I8 sealed through' the glass at the ,upperpartoi the constricted portion or dome I9. of the envelope. and carries a memberI adapted to form the anode of the device.

yOpposed to the'anode and suitably supported by lead-in wire 22, and wirei23 thelower end of which is embedded in press I4 isacathode .generally designated 213 and the details of .which Ahoneycomb construction, preferably formed of with exterior terminal .prongs a the reception metal such as nickel, including the central hollow cylindrical portion 25 from which radial ns 26 project to connect with an outer hollow cylindrical portion '21. Such a cathode is desirably constructed of six cells 28, each of which comprises a segment of the cylindrical portion 25, a pair of radial portions 26 connecting with a segment of the cylindrical portion 21, said outer cylindrical segment projecting beyond the radial portion adjacent its free edge so as to allow for connection with the next cell 28, as by means of spot welding or brazing.

The aforedescribed construction, as illustrated in Fig. 3, means that th'e radial members 26 are of double thickness, as compared with the inner and outer cylindrical portions 25 and 21, and conduct heat from the inner cylindrical portion 25, which receives it directly from the enclosed heater member generally designated 29 and shown enlarged in Figs. 4 and 5, thereby providing for eciently heating all of the walls 25, 26 and 21. The interior surfaces of said walls are desirably coated with electron-emission alkaline-earth material, in accordance with usual practice in making low-temperature electronemitters.

In order to conserve th'e heat of the cathode, the honeycomb structure just described is held in an upwardly opening box 3|, desirably formed as a hollow metal cylinder closed at the bottom only by an upwardly flanged circular metal portion secured thereto as by welding. The metal used may be nickel or iron. I'he box 3| is radially spaced from the cathode 24 by inwardly projecting dimples or generally spherical emboss-V ments 32. This containing box 3| is in turn held in a larger box 33, formed similarly, except as illustrated, and radially and axially spaced therefrom by outwardly projecting dimples or generally spherical corrugations 34 in the box 3|.V

The cathode 24 is in turn spaced axially, as desired, from the bottom of the receiving box 3| by connecting straps 49 of nickel or iron, the upper ends of which are secured to the larger box 33 and the lower ends of which are secured.

to said cathode, as by means of spot welding or brazing.

The outer box 33 is partly closed by an annular flanged member 35, the vertical leg 36 of said member being secured to the upper peripheral portion of the box 33 in any desired manner, as by spot welding, and the lower or horizontal leg 31 projecting inwardly, leaving a constricted opening 38 for the passage of electrons from the cathode. This opening desirably corresponds in size with the opening through associated grids which will be later described. The outer box 33 is directly connected to the lead and support wires, 22 and 23, as by means of spot welding.

The illustrated heater 29, embodying my invention, is received in the central space defined by the hollow cylindrical portion 25 and centered and connected thereto by means of a lower cap member 39, the downwardly projecting peripheral ange 4| of which is secured to the inner cylindrical portion 25 as by means of spot welding, while the upper or annular portion 42 desirably has its inner peripheral portion initially ared, at an angle as indicated at 43, so as to allow for of the heater core 44, of refractory insulating material, such as alumina, beryllia, or magnesia. After assembly said portion 43 may be bent inwardly to grip the restricted portion 5.0i said core, as shown most clearly in Fig. 2.

The upper portion of the heater 29 iS held ill place with respect to the cathode by an upper cap 46, of nickel or the like, with an upwardlir projecting embossment 41 snugly receiving the upper end of said insulator 44 and a depending peripheral flange 48 secured to the upper edge portion of the inner cylindrical part 25 of the cathode 24, as by means of spot Welding. The circuit to the heater filament 53 is from a lead 5| extending from the press |4 and connected to the lower end of the straight or internal portion 52 of said filament 53, the other or lower end of the helical portion of said filament being grounded to the cathode structure, as by spot welding to the depending flange 4|, so that the current passes between the leads 22 and 5| through said filament 53, cathode structure 24 and enclosing boxes 3| and 33.

The core 44 is not only hollow to receive the straight portion 52 of the heater filament 53, but the upper end portion is provided with a slot 50 through which the portion joining the helical and straight portions of the lament 53 passes, as illustrated in Figs. 2, 4 and 5, so that the extreme upper portion of said filament is below the upper cap 45 and thereby insulated therefrom. At the same time the slot 50 correspondingly lightens the core while leaving it strong enough for the purpose.

Between the cathode 24 and anode 2| is a control grid 54 providing a single circular opening 55 for passage of electrons, said opening being coaxial with the cathode and anode. As shown, the grid includes a generally at annular plate 55 with depending fianges 51 and 58. The'outer peripheral flange 58 is connected to a hollow cylindrical radiator member 59, desirably formed of metal, as by means of welding. The control grid 54 is desirably constructed from material of high heat conductivity and melting point.

The discharge between the cathode and anode is desirably conned by shield grid devices comprising a lower hollow cylindrical section 6| around the cathode and extending almost to the grid plate 56, and an upper hollow cylindrical section 62 extending from just above the grid plate 56 to a position well above the anode 2|, said sections being coaxial and of equal diameter. Each shield grid section has a transverse annular baille therein, the lower section having its baille 63 between and parallel to the control grid plate 56 and the plane of the upper edge of the cathode 24, while the upper section has its baille 64 between and parallelto the control grid plate 55 and anode 2| Each baille has an opening therethrough which desirably corresponds in diameter with that of the control grid plate 56 and the cathode baille 35, although this is not essential.

The shield grid sections 6| and 62 are carried by supporting wires 65, in turn carried by a collar applied to the stem I3 and clamped securely thereto. These wires project upwardly on the outside of said shield grid sections in contact with the outer surfaces, being welded or otherwise secured thereto. The wires preferably extend to the upper end of the upper section 62, but an upper end portion of each is desirably left unwelded, thereby enabling the same to be bent outwardly and carry beads 66 to brace the assembly with respect to the dome I9 of the envelope Il, in a 'manner described and claimed in my application,

inner and outer peripheral` videdwithlead-inconductor 61:,1the; construction ofall ofi said grids andthe arrangementand;func@` tion-k Athereof being -moreftfullyr desclirled;V and claimedfinmy` application,Y Serial No'. 503 ,598, filed. September 24, 1943; now mPatentfrNo;` 2,381,632-, dated August .'I, '19.45;

Referring.l now to Fig. 6,v there are shown graphs to support the-statement kthat thezheater givessubstantiallyuniform cathodeheating', that is,'with a minimum temperature gradient from the :top to ithebottom .of :the cathode.. Itis .Well known that the 'maximum= temperature 'of an .ine candescin'g lament'is between the ends or con# nections with'the lead-in conductors;v the :pres-z ence of lead-in conductors Aof lowerV temperature causing theend. portionslof said filament `.to assume a considerably lower temperature.

Thedashdash graphrmarked Temperature of heater filament. represents. 'this conditiornrthe lower end of the filament 55K-being thefcoldest on account of its'connection with the cap .mem-l ber 39. Inasmuch as the upper portion or `upper end of the coiled portion oftheliilament lisintermediate vthe ends of the lament, it has a temperature approaching the maximum; whereby the graph of heater lament temperature 'extends toward higher;temperatures as it goes'from `bottom to near the top.`

On. account of the cathode structure beingopen at the top, even thoughi partly closedby-theV baffle 35, the rate of heat los'svtherefr'omfincreases from the bottom to the top,-as represented by the dotted curve*correspondinglyv marked lin Figi; -6. It will,'therefo're, be seen that the'higher temperature of the heater filament atthe top, partly Vat least, compensates for the'v higher rate offheat loss at thetop than at the bottom, thereby giving a general cathode temperature'substantially constant .as represented by the graph correspondingly marked.

The statement thatfaster heating is provided due to low thermal mass'is clearly shownby'considering` that the onlylpart 'of theheater which takesmuch heat from the heating lament is the single central core member and even this is hollow.` This contrasts with the plurality orinsulative membersI formerly 'employedlin 'connection with heaters of thecharacter disclosed; plus the usual refractory coating of the `outside'of the heatercoil. Of course the member 39 takes some heat Vfrom the refractory'heating flamentbut this is desirable'in order to provide va substantially uni; form general temperature of the 'cathodeyasillustrated in Fig. 6.

From the foregoing vdisclosure it will be seen that I have devised a novel form of cathode heater and cathode containing the same, and although I have shown it enclosed in a thyratron of special construction, it will be understood that said heater is adaptedffor use in or with `many other cathodes, said heater and cathode are adapted for use in many other electron devices, and the arrangementrhere shownris merely illustrative.`

Althougha preferred embodiment oftmypinvention lhas been disclosed; it will be understood that modiflcations'rnaybe made within .the'lspirit and scope of 'theappended claims.

I claim:

l. A cathode comprisingV a hollow element defining `a heater-receivinghspace,v and a heater in said space, said heatercomprising a refractory insulative core, a top cap for said element with a central embossment receiving the top portion of said core, and a refractory metal heating ele- 6` ment'dispose'd'entirelyrbelowsaidacap and helicallyi woundinengagementtwithsaidcore;

2.' A vcathodercomprising. a. 'hollow element` deifiningfa heaterereceivingspace; a heater injsaid space, said heater comprising a refractory- Finsu.-- lativercore"and,1aJ refractory metal heating. elementV onssaid; `core;` a bottomrcap portion `.in saidspace grippingthe core at a groove therein .and with.;a;depending` peripheral ange secured'zto the: lower portion` of said 'cylindrical element, and a Ytoprxcap, vwith a central embossment" receivingl the1top-portionfof .the core and' a kdepending per ripheral .flange secured tothe upper portionof said cylindrical element.

3. A 4cathode comprising a hollow element .dening 'a heater-receiving space,-and a heater in said space,l `saidlheater comprising Va refractory.v insulative core, a topcap forsaid element .witha central'embossment-receiving the top portion of saidacore, .and a refractorymetal heatingfele'- ment engaging said core -along its length, .said element being'a helical-portion on the outside and a stiaigltitl portion running inside of said core, that portion of said element which connects. said helical and straight portions; lying kbelow said cap;

LA cathode comprisingxa hollow elementdeg-f lining; a heater-receivingrspace opening upward-f lyyandaa heater .in-.said space, said heater come prisingfa refractory insulative core and a reir-ac-V tory -rnetal heatingV wire" on said core, said. wire being :formed-as .a helical .portioni engaging vthe outersurface ofr said ,-core; and a straightportion joined' tothe top :end thereof at said core sur-v face and `running insidepf said coregwhereby the greater rate of heat lossK fromfthe top of the heater-receiving space is compensated forfby the highertemperature of the: coil at itstopend, givingv a substantially uniformi operating teme peratureto thef-cathode'fro-mtop to bottom.

5. A cathode-comprising a hollow` cylindrical element defining a r heater-:receivingz space," a heater'in said spacefsaid heatercomprisinga refractoryxinsulative core. and' a refractorymetal heating. element on said core, said felement. being a helical-coil portionron'theoutside and a straight portion'v running inside tof saidcore, a vbottom cap portion :in -said space-- gripping the core -at `a groove ltherein and-:with a depending peripheral flange'lsecured -to the `lower y*portion of said cy'` lindricallelement,v anda top cap with a central embossment lreceiv-ing'the toptportion of thecore and a depending peripheral'angesecured tothe upper lportion 4of said cylindrical element.

6. A l cathode comprising` a hollow cylindrical element defining a heaterfreceiving space', a heater in said spacefsai'd heater comprising a re fractory insulative core i and a vrefractoryl metal heatingelement on-fsaid core; said element being a helical=coilportion ontheroutside and af straight portion*rl-runningA inside` `r-of- 'said 1 core; a bottom cap.- portiorr in vsaid :space-grippingetheicoreL at fa groove vtherein and Withfa *depending peripheral iiangegisecuredl to a the .flower iportiontfof-g 'saidl cy lindrical element,': atop cap with a :centrall em*-y bossment receiving thetop portion: of the'core and 'Y a depending;- peripheral'.- sflangezfsecured 1 to the upper eportioni `of '-saidi cylindrical: element; a plurality` of; electroneemittingupwardly-gwen ing.r cells-:surrounding saidf-heater-'receiving space, anda baille partly closingf therupper A'er'idsof 1.said Ce11S.`::

7. A heater comprising a refractory insulative core, a refractory metal heating element engagingly encircling said core, and conductive means 7 engaging said core above and below portions of said heating elementfor holding said heater 'in place, one end of said heating element being electrically connected to the corresponding heaterholding means.

8. A heater comprising a refractory Ainsulativecore, a filament supported on said core, a portion of said filament being helically Wound about,v and in engagement with, the exterior of said core, another portion being straight and traversing the interior of said core, said core projecting beyond the junction between said helically-wound and straight filament portions, and means formed with a, socket receiving the projecting end portion of said core.

9. A heater, particularly adapted for cathodes of electron devices, comprising a hollow refractory insulative support, a metal cap apertured for receiving said support and with a portion defining said aperture crimped into a restricted portion of said support, and a refractory wire heating element one end of which is connected to said cap and the other end of which passes out of the lower end of said core.

10. A heater, particularly adapted for cathodes of electron devices, comprising a hollow refractory insulative support, a metal -cap apertured for receiving said support and with portions defining said aperture crimped into a restricted portion of said support, and a refractory wire heating element a portion of which is wound on the outside of said core with the lower end connected to said cap and the remainder of which extends from the upper end of said wound portion through the interior of said core, so that the other end of said wire passes out ofthe lower end of said core.

11. A heater comprising a refractory insulative core, a refractory wire heating element, a portion of which is wound on the outside of said core and the remainder of which extends from the upper end of said-wound portion through the interior of said core, said core for that purpose being formed hollow and the upper end portion being slotted from the exterior to communicate with said hollow interior, whereby the'upper portion of said filament in the connection between the helical and straight portions is disposed below the upper end of said core, and an upper cap embossed to receive'the upper en'd portion of said core Without engaging said filament, thereby maintaining electrical insulation between said upper cap and filament.

12. A heater comprising a refractory insulative core, a metal cap apertured to receive said core and with portions defining said apertures crimped into a restricted portion thereof, a refractory wire heating element, a portion of which is wound on the outside of said core with the lower end connected to said cap, and the remainder of which extends from the upper end of said wound portion through the interior of said core, said core for that purpose being formed hollow and the uppe; end portion being slotted from the exterior to communicate with said hollow interior, whereby the upper portion of said filament in the connection between the helical and straight portions is disposed below the upper en'd of said core, and an upper cap embossed to receive the upper end portion ofisaid core without engagingsaid filament, thereby maintaining electrical insulation between said upper cap and filament.

13. An electrical discharge device 'comprising an evacuated envelope, a cathode therein comprising a hollow cylindrical element defining a heater receiving space, a plurality of electron emitting upwardly opening cells surrounding said space, a baille partly closing the upper end of said cells, a heater in said space, said heater comprising a refractory insulative core and a refractory metal heating element, said element being a helical coil portion ony the outside, and a straight portion running inside of said core, a bottom cap in said space gripping the core at a groove therein, and with a depending peripheral flange secured to' the lower portion of said cylindrical element, a top cap with a central embossment receiving the upper portion of said core and a depending peripheral flange secured to the upper portion of said cylindrical element, an electrode adapted to act as an anode and disposed in said envelope opposite side cathode, and grind means disposed between said cathode and anode.

14. A heater particularly adapted for cathodes of electron devices, comprising a hollow refractory insulative support, a. metal cap secured thereto adjacent one end, and a refractory wire heating element, a portion of which engages the outside surface of said core with one end connected to said cap and the remainder of which extends from the other end of said outer portion through the interior of the core.

15. A heater comprising a refractory insulative core, a refractory wire heating element, a portion of which engages the outsidersurface of said core and the remainder of which extends from one end of said outer portion through the interior of saidrcore, said core for that purpose being formed hollow and one end portion slotted along the length from the exterior to the interior, that part of said filament which unites the inner and outer portions thereof passing through said slotted portion intermediate the core ends.

16. A cathode comprising a hollow element defining a heater-receiving space, and a heater in said space, said heater comprising 'a refractory insulative'generally hollow cylindrical core and a refractory metal heating element, a por# tion of which is wound on the outer cylindrical surface of said core and lies in engagement therewith, another portion of 'which runs along the hollow interior of said core, and a third portion of which is disposed intermediate the ends, and passes through a side of, said core, and connects said helical and interior portions.

WARD W. WATROUS, JR.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,991,197 Denzler Feb. 12, 1935 1,936,048 Crowley Nov. 2l, 1933 1,942,080 Young Jan. 2,1934 1,368,584 Torrisi Feb. 15, 1921 1,797,990 Lucian Mar. 24, 1931 FOREIGN PATENTS Number Country Date 404,646 Great Britain Jan. 11, 1934 37,515 Netherlands Feb. 15, 1936 

